Mosquitoes and black flies are representative of the order Diptera which are pests that have plagued humans and animals for generations. Mosquitoes are the major vectors for a number of human and animal diseases, including malaria, yellow fever, viral encephalitis, dengue fever and filariasis.
Various chemical pesticides have been developed with the goal of controlling Diptera. For example, treatment of a water source with a water-soluble alcohol in water-miscible form for mosquito abatement is disclosed in U.S. Pat. No. 6,077,521. However, more recent emphasis has been placed on the use of biopesticides. For example, controlled-release formulations of at least one biological pesticidal ingredient are disclosed in U.S. Pat. No. 4,865,842; control of mosquito larvae with a spore-forming Bacillus ONR-60A is disclosed in U.S. Pat. No. 4,166,112; novel Bacillus thuringiensis isolates with activity against Dipteran insect pests are disclosed in U.S. Pat. Nos. 5,275,815 and 5,847,079; a biologically pure culture of a Bacillus thuringiensis strain with activity against insect pests of the order Diptera is disclosed in U.S. Pat. No. 5,912,162 and a recombinantly derived biopesticide active against Diptera including cyanobacteria transformed with a plasmid containing a B. thuringiensis subsp. israelensis dipteracidal protein translationally fused to a strong, highly active native cyanobacteria's regulatory gene sequence is disclosed in U.S. Pat. No. 5,518,897.
Yet even these biopesticides have drawbacks; so the search for new biopesticides continues. One drawback of certain biopesticides is the potential build-up of pesticidal resistance.
Resistance is defined by differences in susceptibility that arise among populations of the same species exposed to a pesticide continuously over a period of time. These differences are identified by observing a statistical shift in the lethal dose (LD) either to kill 50% or 95% of the population (LD50 or LD95 respectively). Individual differences in susceptibility exist within each species, and pests that are substantially less susceptible may be present, generally at low frequencies, in at least some of the wild populations. In the presence of the pesticide, it is these substantially less susceptible pests that survive and reproduce. Since their ability to survive is a result of their genetic makeup, their resistant genetic makeup is then passed on to their offspring, resulting in shifts in the populations' susceptibility via pesticide-induced selection. Resistance to larvicides has been encountered among certain Dipteran species.
Specifically, the development of resistance in Culex quinquefasciatus to Bacillus sphaericus (B.s.) is noted by Rodcharoen et al., Journal of Economic Entomology, Vol. 87, No. 5, 1994, pp. 1133-1140. A method for overcoming this resistance, by combining B.s. with purified Cyt1A crystals isolated from Bacillus thuringiensis subsp. israelensis or by combining a recombinant B.t.i. with B.s., is disclosed by Wirth et al., Journal of Medical Entomology, Vol. 37, No. 3, 2000, pp. 401-407. However, improved but naturally derived or occurring biological larvicides and compositions to overcome Culex mosquito resistance to B.s. applications would be desirable. It is even more desirable if the biological Larvicide composition has the ability to effectively control broad spectrum mosquito species.